Yes, real world helps these discussions which I why I'm using full frame DSLR prime lenses that exist rather than attempting to compare APS-C mirrorless prime lenses to APS-C DSLR prime lenses that do not exist.

What mirror-less camera are you using for this comparison, and why? Because they are more comparable to FF cameras than to APS-C versions?

Does it matter? I'm referring to APS-C mirrorless lenses that exist. That means Sony, Fuji, Canon, and Fuji. Somewhere along the lines we were talking about m4/3 lenses and even some full frame mirrorless (Leica) lenses.

Leica is under consideration (for that matter any FF lens) because they can be used on these mirror-less cameras. But the issue is your dismissal of comparing APS-C mirror-less to APS-C DSLR. It is inconvenient enough for you to, in fact, run away to FF format where we don't have much of mirror-less presence (at this time) at least not counting Leica.

It seems that we are not understanding each other as you keep bringing up things which I consider irrelevant and I say things which you don't understand.

I'll try to clear things once more then I may just need to bow out of this discussion.

This whole series of post started with the claim that mirrorless wide angle lenses can be made "very small" compared to the DSLR lenses. I disputed that claim referencing several small DSLR wide angles and pointed out how most mirrorless wide angles are only small due to their small apertures (relative to full frame DSLR lenses). Leica lenses do show that you can make a smaller ultra-fast wide angle for mirrorless but it's not much smaller and at least in the case of Leica, the price is massive.

You seem to think I'm dismissing comparing APS-C DSLR lenses to APS-C mirrorless lenses. I'm not dismissing it. I'm admitting that APS-C DSLRs fail to deliver on smaller lenses when equivalent apertures are considered just like mirrorless APS-C (and m4/3 for that matter) fail to deliver as well.

I'm making comparisons where they can be made, i.e. looking at an existing APS-C/m4/3/Leica mirrorless prime/zoom and talking about it's equivalent lens in full frame DSLR terms.

Yes, I have no problems admitting that APS-C DSLR lenses lose to mirrorless APS-C lenses frequently when there are comparable lenses to evaluate.

Well, according to you, mirror-less cameras are already winning the battle when their sensor size is matched to DSLR.

I'm talking about lenses, not bodies. Why do you keep bringing up bodies?

What are you using lenses for, while you dismiss sensor size as being unimportant?

I don't even know how to respond to this. I don't know why you keep bringing up the size of a particular camera body when we are trying to discuss the size of lenses. Maybe you are just intentionally trying to confuse/frustrate me. It's working.

But the latter loses to full frame DSLR lenses when you compare true equivalents.

And what would comprise these "true equivalents"?

Equal field of view and equal aperture size...

So, you're using "bodies". You need to make up your mind first. Fidgeting around gets a discussion nowhere.

BTW, what exactly is "equal aperture size"?

One last time:

25mm on m4/3 gives a 44 degree angle of view. A 25mm f/1.4 lens has a 17.8mm aperture.

50mm on FF gives a 44 degree angle of view. A 50mm f/1.4 lens has a 35.7mm aperture.

In order to make a m4/3 lens truly equivalent to a 50mm f/1.4 on full frame, you'd need a 25mm f/0.7. In order to have a FF lens equivalent to a 25mm f/1.4 lens on mirrorless, you'd need a 50mm f/2.8 lens.

Which do you think will be cheaper/smaller? For reference, 50/1.8 lenses for FF sell for $100-200 right now. The Panasonic 25mm f/1.4 is $500. The Nikon 50mm f/1.8G is about the same size and weight as the Panasonic.